In broadband wireless networks the general assumption in existing receivers is that all received code blocks must be decoded. Decoding of forward error correction (FEC) codes (such as turbo codes) is a very expensive operation that consumes a significant amount of power in the receiver of a communications system. Operation of the FEC decoder, particularly inefficient operation of the FEC decoder when signal conditions or channel quality is poor, directly impacts power consumption and particularly battery life of the mobile wireless communications device.
Broadband wireless communication systems such as Universal Mobile Telecommunications System (UMTS), High-Speed Downlink Packet Access (HSDPA) or 3GPP Long-Term Evolution (LTE) wireless networks employ Hybrid-ARQ (automatic repeat request) error control method in the receive path to improve the ability of the decoder to successfully decode in poor signal conditions. With HARQ each code block (or set of code blocks) has a set of parity bits from a cyclic redundancy check (CRC) appended to the information bit stream. These parity bits allow the receiver of the mobile wireless communications device to determine if the set of hard bit decisions is correct. Subsequent to the decoding and CRC check the receiver sends a message to the transmitter 102 indicating the success of the decoding. If the CRC passes a positive acknowledgment is transmitted (an ACK). If the CRC fails the receiver sends a negative acknowledgment (NAK) to the transmitter 102. The transmitter 102 upon reception of a NAK will retransmit a subset of the bits in the code block. The receiver will then combine these retransmitted bits with the information from the original transmission and attempt a second decoding. With each retransmission the probability of successfully decoding the transmission is increased as the signal energy is accumulated and the benefits of diversity are realized. This retransmission process may be repeated several times until the decoding succeeds or some maximum number of retransmissions has been reached. During this process the decoder may still be processing code blocks with little or no potential success of decoding and the FEC decoder utilizes resources to decode blocks with low probability of success. The inefficient operation of the FEC decoder has a direct impact on power consumption of the communications device and particularly the battery life in a mobile wireless communications device.
Therefore there is a need for improved utilization of the FEC decoder in the receiver of communication devices.
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.